A Spanish major might sound like "leg up" but I would strongly suggest you choose a science major or double major with a science.
My advice is bias and based on personal experience, however I really wish someone told me to major in biology or chemistry, instead of wasting time on a nutrition degree. I actually had an academic advisor tell me to stick with nutrition because the major is "different" and it will make you "stand out" as an applicant.. I have no idea how adcoms view ones major, but I am almost certain that no body cares what your major is in as long as you do well in your classes and subsequently score well on the mcat. Not only does a science major allow you to mingle with other premeds at school, but it also gives you a significant advantage when you study for the mcat. Although nutrition is an associated science, classes like genetics, cell bio, etc were not required for us. This was something I personally struggled with when it came to mcat prep, and something to this day I still regret. I can't even imagine the struggle as a non-science major.
Again my advice is bias and if anyone has insight on how adcoms view an applicant's major I am curious. I think Its great that you are interested in Spanish but instead of dedicating your major to it you should get involved in Spanish related ECs (and totally learn the language on your own! From my experiences schools really appreciate a bilingual ability)